Traveling wave tube

ABSTRACT

A traveling wave tube amplifier having an axial annular electron stream and a pair of counterwound axially aligned and radially spaced helices positioned intermediate the electron beam source and the collector electrode. The innermost helix is wound on the outer surface of a cylindrical ferrite which in turn is biased by means of a current-carrying wire loop passing through the axial bore of the ferrite cylinder. The RF input to the amplifier is at the electron source end and is applied to both counterwound coils, either in-phase or 180* out-of-phase. The annular electron stream passes through the annular spacing between both helices and interacts with a prescribed mode, preferably the fundamental mode of RF wave energy propagated axially along the ferrite cylinder.

United grates Patent Jasper, Jr.

[5 TRAVELING WAVE TUE Primary ExaminerNathan Kaufman Attorney-Harry M. Saragovitz, Edward J. Kelly, Herbert Berl [72] Inventor. Louis J. Jasper, Jr., Neptune City, NJ. and Jack H Stanley [73] Assignee: The United States of America as represented by the Secretary of the Army [57] ABSTRACT 2] Filedi P 1970 A traveling wave tube amplifier having an axial annular elec- 21 L N 32 6 5 tron stream and a pair of counterwound axially aligned and 1 App 0 8 radially spaced helices positioned intermediate the electron beam source and the collector electrode. The innermost helix U-S. 3 is wound on the outer urface of a cylindrical ferrite in [51] Int. Cl. ..H03f 3/58 [um is biased by means f currem carrying wire loop passing [58] Fleld of Search ..330/43; 3l5/3.6 through the axial bore of the ferrite cylinder. The RF input to the amplifier is at the electron source end and is applied to [56] References C'ted both counterwound coils, either in-phase or 180 out-of- UNn-ED STATES PATENTS phase. The annular electron stream passes through the annular spacing between both helices andinteracts with a Branch, 11'. rescribed mode preferably the fundamental mode of 21885 ,593 5/ 1959 Cook 15/3-6 wave energy propagated axially along the ferrite cylinder. 2,925,565 2/1960 Cook et a1 ..3l5/3.6X

l 1 Claims, 2 Drawing Figures OUTPUT 32 2s 4,

A I\ Y\\ l6 I8 4 028 "1/ 3e 34 la INPUT PATENTED APR 4 I972 OUTPUT INPUT FIG. 1

FIG. 2

INVENTOR, LOUIS J. JASPER Jr.

W H AGENT BY r 2% ATTORNEYS.

TRAVELING WAVE TUBE The invention described herein may be manufactured, used,

and licensed by or for the Government for governmental purposes without the payment to me of any royalty thereon.

BACKGROUND OF THE INVENTION This invention relates to traveling wave tube amplifiers and more particularly to an improved double-coupled helix traveling wave tube.

In traveling wave interaction devices where energy is exchanged between an electron stream and propagated wave, the average velocity of the electron stream is usually somewhat greater than that of the propagated wave so that energy is transferred to the propagated wave from the electron stream. As a result, amplification of the propagated wave is achieved. One of the factors controlling the efficacy of such tubes is a function of the gain per unit length of the interaction medium and, while various systems have been proposed to increase the gain per unit length, no system has proved to be entirely satisfactory,

SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved traveling wave tube wherein the gain per unit length is increased.

It is another object of the present invention to provide an improved traveling wave tube wherein the improvement in gain per unit length is accomplished by utilizing a cylinder of ferrite material in the interaction region of the tube.

In accordance with the present invention there is provided a traveling wave tube which utilizes interaction between a traveling electromagnetic wave and an electron stream. Included is a wave interaction circuit comprising a cylindrical ferrite element, a first helix wound on the surface of the cylindrical ferrite and a second helix counterwound with respect to the first helix and radially spaced therefrom. Also included are means for forming an annular electron stream for flow axially through the annular spacing between the helices. In addition there is included discrete means for coupling an RF signal to said helices whereby an electronmagnetic wave is propagated axially along said cylindrical ferrite surface and interacts with said annular stream.

BRIEF DESCRIPTION OF THE DRAWING For a better understanding of the invention, together with other and further objects thereof, reference is made to the following description taken in connection with the accompanying drawing in which:

FIG. I is a view, partly in section, of a preferred embodiment of a traveling wave tube constructed in accordance with this invention; and

FIG. 2 is a transverse section taken along lines 2-2 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT For purposes of clarity all the conventional voltages have been omitted from FIG. 1.

Referring now to FIGS. 1 and 2 of the drawing, at there is shown a traveling wave amplifier tube having an elongated metallic envelope 12 which is evacuated in the conventional manner. At one end of tubular envelope 12 is an electron gun structure 14 for producing an annular electron stream 16. Electrons emitted by the electron gun 14 are directed to a collector plate or anode 18 at the other end of envelope l2. Centrally and longitudinally positioned with envelope l2 intermediate electron gun 14 and collector anode 18 is a cylinder or tubular element 20 made of a suitable ferrite material well known in the art and having an axial bore 22. A d-c biasing coil 24 extends through the central bore 22 of ferrite cylinder 20 and is terminated by a suitable d-c voltage source (not shown) positioned outside of envelope 12. The applied bias to ferrite cylinder 20 through current-carrying coil 24 is such as to provide a circumferential or transverse magnetic field in ferrite cylinder 20 which extends slightly beyond the outer surface of ferrite cylinder 20.

A first or inner helix 26 is uniformly wound on the outer surface of ferrite cylinder 20 at a prescribed pitch angle with respect to the longitudinal axis of envelope 12. The input lead 28 of inner helix 26 is at the electron gun end of tube 10 and the output lead 30 of inner helix 26 is at the collector end of tube 10. A second or outer helix 32 surrounds inner helix 26 and is radially spaced therefrom. Helix 32 is counterwound with respect to helix 26 at a pitch angle approximately equal, but opposite, to the prescribed pitch angle of helix 26. Any conventional means such as the longitudinal dielectric rods 34 may be used to support outer helix 32 in radially spaced position relative to inner helix 26. As shown, the annular electron stream 16 is concentrated between the annular spacing between helix 26 and helix 32. Input lead 36 of helix 32 is at the electron gun end of tube 10 and the output lead 38 of helix 32 is at the collector end of tube 10. A longitudinal or axial magnetic field indicated by the arrow labeled H may be provided by any suitable manner well known in the art such as a solenoid. Input leads 28 and 36 of respective helices 26 and 32 are connected to an input RF signal source 40 which may provide two substantially equal amplitude RF signals in-phase or out-of-phase, as desired. Output leads 30 and 38 of respective helices 26 and 32 are connected across the output circuit 42. As conventionally understood, both helices are maintained substantially at the same potential as that of collector anode 18.

In considering the operation of the traveling wave tube as an amplifier, it is preferable to provide substantially equal amplitude, but 180 out-of-phase, RF signals as the respective inputs to helices 26 and 32. Any well known wide-band phase shifter may be utilized to produce such signals. The continuous dc bias applied to cylindrical ferrite 20 through coil 24 is adjusted to provide an effective permeability such that the RF or electromagnetic wave energy propagated along the helices 26 and 32 is not absorbed by the ferrite cylinder 20 but is reflected from the outer surface thereof. This may readily be achieved by operating ferrite cylinder 20 in a low-loss region of the absorption curve preferably above the low field loss region but below ferromagnetic resonance.

As a result, the dominant mode supported by the tube provides a radial electric field which is concentrated in the annular spacebetween helix 26 and helix 32. This type of RF mode is commonly referred to as the transverse mode. Due to the counterwound helixes, strong coupling is achieved therebetween and maximum interaction will occur between the transverse RF mode and the annular electron stream 16 to proide forward wave signal amplification. The biasing of the cylindrical ferrite 20 controls the velocity of the transverse RF electromagnetic wave propagated through the ferrite. With transverse mode operation, maximum interaction may be achieved with one of the existing synchronous waves, for example, to provide increased efficiency inasmuch as there is a concomitant minimum velocity modulation of the beam for the synchronous waves.

In another mode of operation, referred to as the longitudinal mode, the respective input RF signals are applied inphase to the helices 26 and 32. This mode of operation produces a strong longitudinal or coaxial RF field which interacts with annular stream 16. Longitudinal mode operation yields high interaction impedance and hence greater gain for a given length.

We wish it to be understood that we do not desire to be limited to the exact details of construction shown and described, for obvious modifications will occur to a person skilled in the art.

What is claimed is:

1. In a traveling wave tube utilizing interaction between a traveling electromagnetic wave and an electron stream,

a wave interaction circuit comprising an inner cylindrical ferrite element,

a first helix wound on the outer surface of said cylindrical ferrite,

a second helix of larger dimensions than said first helix and radially spaced from said first helix, said helices being counterwound,

means for forming an annular electron stream for flow axially through the annular spacing between said helices,

and discrete means for coupling an input RF signal to said helices whereby an electromagnetic wave is propagated along said ferrite surface and interacts with said annular stream.

2. The device in accordance with claim 1 wherein said cylindrical ferrite includes an axial bore and d-c current carrying means passing through said bore for biasing said cylindrical ferrite.

3. The device in accordance with claim 2 wherein the input RF signals to said first and second helices are substantially equal in amplitude and in-phase.

4. The device in accordance with claim 2 wherein the input RF signals to said first and second helices are substantially equal in amplitude and 180 out-of-phasei 5. The device in accordance with claim 2 wherein said ferrite cylinder is d-c biased such that a dominant transverse mode of RF wave is propagated along the surface of said fer rite intermediate said helices.

6. The device in accordance with claim 1 wherein said first and second helices are wound such that pitch of said first helix is substantially equal to but opposite to the pitch of said second helix.

7. The device in accordance with claim 6 wherein said ferrite cylinder includes an axial bore and d-c current carrying means passing through said bore for biasing said cylindrical ferrite.

8. The device in accordance with claim 6 wherein the input RF signals to said first and second helices are substantially equal in amplitude and in-phase.

9. The device in accordance with claim 6 wherein the input RF signals to said first and second helices are substantially equal in amplitude and out-of-phasel 10. The device in accordance with claim 1 wherein the input RF signals to said first and second helices are substantially equal in amplitude and in-phase.

11. The device in accordance with claim 1 wherein the input RF signals to said first and second helices are substantially equal in amplitude and 180 out-of-phase. 

1. In a traveling wave tube utilizing interaction between a traveling electromagnetic wave and an electron stream, a wave interaction circuit comprising an inner cylindrical ferrite element, a first helix wound on the outer surface of said cylindrical ferrite, a second helix of larger dimensions than said first helix and radially spaced from said first helix, said helices being counterwound, means for forming an annular electron stream for flow axially through the annular spacing between said helices, and discrete means for coupling an input RF signal to said helices whereby an electromagnetic wave is propagated along said ferrite surface and interacts with said annular stream.
 2. The device in accordance with claim 1 wherein said cylindrical ferrite includes an axial bore and d-c current carrying means passing through said bore for biasing said cylindrical ferrite.
 3. The device in accordance with claim 2 wherein the input RF signals to said first and second helices are substantially equal in amplitude and in-phase.
 4. The device in accordance with claim 2 wherein the input RF signals to said first and second helices are substantially equal in amplitude and 180* out-of-phase.
 5. The device in accordance with claim 2 wherein said ferrite cylinder is d-c biased such that a dominant transverse mode of RF wave is propagated along the surface of said ferrite intermediate said helices.
 6. The device in accordance with claim 1 wherein said first and second helices are wound such that pitch of said first helix is substantially equal to but opposite to the pitch of said second helix.
 7. The device in accordance with claim 6 wherein said ferrite cylinder includes an axial bore and d-c current carrying means passing through said bore for biasing said cylindrical ferrite.
 8. The device in accordance with claim 6 wherein the input RF signals to said first and second helices are substantially equal in amplitude and in-phase.
 9. The device in accordance with claim 6 wherein the input RF signals to said first and second helices are substantially equal in amplitude and 180* out-of-phase.
 10. The device in accordance with claim 1 wherein the input RF signals to said first and second helices are substantially equal in amplitude and in-phase.
 11. The device in accordance with claim 1 wherein the input RF signals to said first and second helices are substantially equal in amplitude and 180* out-of-phase. 